1. Field of the Invention
This invention relates to functional fluids thickened with associative polyether thickeners. In addition to the associative polyether thickener, the fluids also contain a dialkyldithiophosphate, a compound which is a source of molybdate ion, a polyether nonionic surfactant, and other optional ingredients.
2. Description of the Prior Art
It is known to formulate functional fluids with associative polyether thickeners. See, for instance, U.S. Pat. Nos. 4,411,819 and 4,312,768. However, the fluids described in these patents have wear rates of approximately 20 milligrams per hour. Because of the high wear, these fluids are not entirely satisfactory in pumps which may operate at higher pressures (greater than 500 psi).
It is also known that dialkyldithiophosphate and molybdenum containing compounds can be used separately as additives in functional fluids to improve their wear properties. However, these wear additives are not as effective as wear additives when compared to metal dialkykldithiophosphates.